1. Field of the Invention
The present invention relates to a mammograph equipped with an integrated device for taking stereotaxic photographs as well as to a method of utilization of said mammograph. The invention is primarily applicable to the medical field in which mammography appears to be the best means of preventive detection or treatment of breast cancer. Stereotaxic photographs are photographs which serve to determine by computation the position of a tumor or of a lesion within a breast under examination.
2. Description of the Prior Art
A mammography apparatus is mainly composed of an arm which is capable of moving about an axis and carries an x-ray generator tube at one end and an image receiver at another end. In the majority of instances, the image receiver comprises a cassette provided with a film and an image intensifier screen. Different devices are interposed on the path of the beam of x-radiation emitted by the tube. Provision is normally made for a beam limiter located upstream in proximity to the x-ray tube. Further downstream and in proximity to a breast support plate, there is provided a breast compression cushion or plate. Said breast support plate and said compression plate are intended to hold the breast in position at the moment of taking of x-ray photographs. They are normally rigidly fixed to the x-ray tube and to the receiver but can be detached therefrom. The fact that the x-ray tube and the image receiver are capable of moving in rotation, if necessary around the breast support plate and compression plate or in fixed relation to these latter makes it possible to take stereotaxic photographs.
In order to produce these stereotaxic photographs, the following procedure is adopted. A second image receiver is employed and fixed near the breast support plate. The x-ray tube which is rigidly fixed to the first image receiver is inclined in a first orientation with respect to the alignment of the breast support plate and the compression plate, a cassette is introduced into the second image receiver and a first photograph is taken. For the first photograph, the cassette is displaced laterally on one side in the second image receiver, with the result that only a first lateral portion of the film contained therein is printed from the first exposure. The cassette is then displaced to the other side within the image receiver, the x-ray tube is inclined in a second orientation and a second photograph is taken. The film corresponding to the two exposures is subsequently developed and, by means of a stereotaxic locating device, the principle of operation of which involves computer processing of the two images obtained, the spatial position of any tumor which may be present is determined, whereupon a biopsy needle is guided with accuracy for therapeutic purposes.
A mammography examination is a relatively unpleasant ordeal for the patient. It is therefore important to take rapid action. On the contrary, the devices in accordance with the present state of the art as described in the foregoing in fact suffer from a disadvantage in that they are slow since it is necessary to displace the cassette between exposures, to develop the film, to compute the position, and to guide the needle, before compression on the breast can be relieved. In the first place, known devices are thus not easy to handle and, in the second place, have a traumatizing effect on patients.
However, these known devices have a wide range of different functions. In particular, they must make it possible to take pictures of the breast at different angles of incidence and especially vertical angles of incidence. It is therefore important to ensure that equipment which is capable of solving the handling problems referred-to above does not do so at the expense of the possibilities of utilization of devices of known type.
When use is made of a larger film cassette which is displaced between the two photographs, the two photographs are not superposed at the two angles of incidence. However, this technique makes it necessary on the one hand to have a zero position reference on each photograph and on the other hand to provide a larger cassette holder in the image receiver. This latter must in fact have a width equal to the length of the cassette plus the length of displacement which is necessary. This may be a cause of difficulty when placing the patient in position, in particular at oblique incidence.
The invention is intended to overcome these disadvantages by proposing two movable elements for supporting the mammograph accessories. These two elements are capable of moving on the one hand with respect to the general support of the mammograph and on the other hand with respect to each other. One of these movable elements carries the x-ray tube whilst the other carries the remainder of the accessories, namely the compression plate, the breast support plate and the single image receiver. The image receiver is thus separated from the x-ray tube. In order to take stereotaxic photographs, the image receiver is also moved aside and this accordingly offers the advantage of a parallax effect which results from relative displacement in projection of the image of a fixed object projected on a fixed image receiver, when the center of projection has moved. The position of the x-ray tube is then simply moved through a predetermined angle which is sufficient to ensure that the two projected images of the breast under radiographic examination are juxtaposed. In order to make this separation of images even more effective, the procedure adopted consists in moving the image receiver away from the breast under radiographic inspection to a distance which is a function of the variation in inclination of the x-ray tube.